Plasmon‐Mediated Nanocathode for Synchronized Generation of Picosecond Pulsed Electron Beam and Electromagnetic Radiation

Vacuum electronic devices offer superior electron mobility and spatiotemporal electron manipulating precision, with recent challenges focusing on ultrafast electron pulses for high-frequency, high-energy, and high-resolution applications. Plasmon-mediated electron emission (PMEE) nanocathodes provide a promising solution by producing high-quality ultrafast electron pulses while simplifying the electron beam manipulation. In this study, we developed a PMEE Au-on-Gr nanocathode using vertically aligned few-layer graphene decorated with gold nanoparticles, enabling synchronized generation of picosecond pulsed electron beam and electromagnetic radiation. The nanocathode achieved 80 MHz electron pulses with a 500 ps pulsewidth, 0.91 A·cm^-2 peak current density, 6.53% external quantum efficiency, and 8.81 × 10⁹ A·m^-2·sr^-1·V^-1 reduced brightness. Additionally, it exhibited a 7.1° divergence angle and 0.97 eV energy spread under low excitations. Synchronized radiation pulses at 2.3, 5.7, and 9.2 GHz corresponded to electron pulse features. The excellent performance stems from plasmonic field enhancement and efficient hot electron generation driven by localized surface plasmon resonance (LSPR) in the PMEE nanocathode. The dynamic effects of high-energy hot electron injection at the Au-Gr interface also play a critical role. This system enables compact, room-temperature, low-power vacuum electronic devices for ultra-high spatiotemporal resolution and high-frequency applications, driving progress in materials science and nanotechnology.